In recent years, there is a growing demand for a method of producing scroll fluid machines which method improves working precision and reduces the period of time required for working.
FIG. 6 illustrates a scroll compressor which is one kind of scroll fluid machine. A scroll blade 11 of the scroll compressor is generally formed of cast iron or steel to obtain a required strength, and is formed mainly by cutting (machining) through an end mill etc., to meet a required precision. In many cases, scroll blades are formed by using spheroidal graphite cast iron and by cutting through an end mill used for as the finish-working thereof.
Since a scroll blade has a complicated shape as shown in FIG. 3 and must be formed with a high precision, it usually takes a very long time to work it, e.g., cut it by means of an end mill. Therefore, in order to reduce the production costs of a scroll fluid machine, it is necessary to produce scroll blade with a low cost.
To reduce the period of time required to form a scroll blade, it is necessary to increase the cutting rate of a working such as that of an end mill. The cutting rate can be increased by increasing the cutting amount per rotation of the tool and/or by increasing the rotational speed of the tool.
Since increasing of the cutting amount per rotation of a tool such as an end mill generally causes reduction of working precision, the cutting amount per rotation cannot be substantially increased in the production of scroll blades, which requires a high working precision. Therefore, in the production process of scroll blades, the rotational speed of a cutting tool such as an end mill must be increased in order to reduce the period of time and the number of steps necessary to form a scroll blade. However, if a cutting tool is used at an increased rotational speed, the service life of the tool is reduced, which means an increase in the period of time and the number of steps due to the exchange of cutting tools during production of scroll blades, resulting in a low productivity. In practice, an appropriate balance between the working precision and the time necessary to produce a scroll blade is sought to reduce the production costs of the scroll blade.
Similarly, in a case where castings are used to form scroll blades, the period of time and the number of steps necessary to work-finish a scroll blade are significant and, therefore, productivity is low. In general, a well-balanced working regarding all of the working precision, the period of working time and the volume to be machining-removed is important to reduce the production costs of a scroll blade.